Re: [PATCH net-next V2 00/11] net/mlx5e: Add support for devmem and io_uring TCP zero-copy

Dragos Tatulea
2025-05-28T09:17:12Z

On Tue, May 27, 2025 at 09:05:49AM -0700, Stanislav Fomichev wrote:
> On 05/23, Tariq Toukan wrote:
> > This series from the team adds support for zerocopy rx TCP with devmem
> > and io_uring for ConnectX7 NICs and above. For performance reasons and
> > simplicity HW-GRO will also be turned on when header-data split mode is
> > on.
> >
> > Find more details below.
> >
> > Regards,
> > Tariq
> >
> > Performance
> > ===========
> >
> > Test setup:
> >
> > * CPU: Intel(R) Xeon(R) Platinum 8380 CPU @ 2.30GHz (single NUMA)
> > * NIC: ConnectX7
> > * Benchmarking tool: kperf [1]
> > * Single TCP flow
> > * Test duration: 60s
> >
> > With application thread and interrupts pinned to the *same* core:
> >
> > |------+-----------+----------|
> > | MTU | epoll | io_uring |
> > |------+-----------+----------|
> > | 1500 | 61.6 Gbps | 114 Gbps |
> > | 4096 | 69.3 Gbps | 151 Gbps |
> > | 9000 | 67.8 Gbps | 187 Gbps |
> > |------+-----------+----------|
> >
> > The CPU usage for io_uring is 95%.
> >
> > Reproduction steps for io_uring:
> >
> > server --no-daemon -a 2001:db8::1 --no-memcmp --iou --iou_sendzc \
> > --iou_zcrx --iou_dev_name eth2 --iou_zcrx_queue_id 2
> >
> > server --no-daemon -a 2001:db8::2 --no-memcmp --iou --iou_sendzc
> >
> > client --src 2001:db8::2 --dst 2001:db8::1 \
> > --msg-zerocopy -t 60 --cpu-min=2 --cpu-max=2
> >
> > Patch overview:
> > ================
> >
> > First, a netmem API for skb_can_coalesce is added to the core to be able
> > to do skb fragment coalescing on netmems.
> >
> > The next patches introduce some cleanups in the internal SHAMPO code and
> > improvements to hw gro capability checks in FW.
> >
> > A separate page_pool is introduced for headers. Ethtool stats are added
> > as well.
> >
> > Then the driver is converted to use the netmem API and to allow support
> > for unreadable netmem page pool.
> >
> > The queue management ops are implemented.
> >
> > Finally, the tcp-data-split ring parameter is exposed.
> >
> > Changelog
> > =========
> >
> > Changes from v1 [0]:
> > - Added support for skb_can_coalesce_netmem().
> > - Avoid netmem_to_page() casts in the driver.
> > - Fixed code to abide 80 char limit with some exceptions to avoid
> > code churn.
>
> Since there is gonna be 2-3 weeks of closed net-next, can you
> also add a patch for the tx side? It should be trivial (skip dma unmap
> for niovs in tx completions plus netdev->netmem_tx=1).
>
Seems indeed trivial. We will add it.

> And, btw, what about the issue that Cosmin raised in [0]? Is it addressed
> in this series?
>
> 0: https://lore.kernel.org/netdev/9322c3c4826ed1072ddc9a2103cc641060665864.camel@nvidia.com/
We wanted to fix this afterwards as it needs to change a more subtle
part in the code that replenishes pages. This needs more thinking and
testing.

Thanks,
Dragos